Image scaling is commonly used in computer graphics to resize digital images. The scaling process is far from trivial, since it involves a trade-off between efficiency, smoothness and sharpness. As the size of an image is increased, the pixels which form the image become increasingly visible, making the image appear soft. Conversely, reducing the size of an image will tend to enhance its smoothness and apparent smoothness.
Various different image scaling methods exist and are well known to those skilled in the art. One such method is nearest-neighbour interpolation, whereby each pixel in an image is replaced with multiple pixels of the same colour. Other, more complex methods include linear or bilinear interpolation, bicubic interpolation and supersampling, to name but a few. While some of these image scaling methods are better at preserving smooth contours in the image, others may be simpler and less costly to implement.
When it comes to image transmission, some form of compression (also referred to as encoding) is often applied to the image streams in order to reduce data storage volume and bandwidth requirements. It is known to use a quincunx or checkerboard pixel decimation pattern in video compression. In commonly assigned US patent application publication 2003/0223499, stereoscopic image pairs of a stereoscopic video are compressed by removing pixels in a checkerboard pattern and then collapsing the checkerboard pattern of pixels horizontally. The two horizontally collapsed images are placed in a side-by-side arrangement within a single standard image frame, which is then subjected to conventional image compression (e.g. MPEG2). The decompressed standard image frame is then expanded into the checkerboard pattern and the missing pixels are spatially interpolated.
One stumbling block that has arisen in the course of implementing such image compression is that the inherent nature of the encoding may make it impossible to scale compressed image frames. More specifically, when frames of a compressed image stream are formed by arranging pixel mosaics in side-by-side or above-below arrangements, any scaling of these frames leads to artifacts (e.g. visual jagged lines) in the image frame after decompression. The scaling actually disrupts the encoding (decimation pattern) to the point that, upon decompression, the quality of the resulting image is degraded and unacceptable, irrespective of the scaling method used.
Consequently, there exists a need in the industry to provide a method for scaling compressed image frames without inducing significant artifacts in the frames upon decompression.